Method and apparatus for the diagnosis of polyneuropathy syndromes

ABSTRACT

A method and/or an apparatus for the determination of whether a subject has nerve damage (polyneuropathy) and/or the degree of the nerve damage is characterized in that an increase of the skin temperature is provoked at an extremity of the subject, that at the same time perfusion value or a value correlated with this perfusion value is measured at this extremity, and the time from the start of the increase in temperature of the skin up to the start of an increase in perfusion as a result of the elevated skin temperature is evaluated as a measure for the presence and/or the degree of the nerve damage.

This is a continuation of application Ser. No. 07/445,724, filed Dec. 1,1989, now U.S. Pat. No. 5,191,895.

The present invention relates to a method and an apparatus fordetermining whether a subject has nerve damage (polyneuropathy) and/orthe degree of the nerve damage.

With numerous diseases polyneuropathy syndrom (PNS) arises as a frequentcomplication. Above all diabetes mellitus should be named here. In anextensive investigation by Canal et al. (Canal N, Pozza G(eds):Peripheral neuropathies. Elsevier North-Holland, Amsterdam, pages 247 to255) it was found that after a period of more than five years forpatients requiring insulin for diabetes mellitus only 18% were still notsuffering from a manifest polyneuropathy syndrome. As further frequentcauses consideration should be paid, above all, to other metabolicdisturbances, such as for example in the context of chronic alcoholism(ethylismus) with various poisons or also neoplastic and inflamatoryprocesses.

The clinical study of PNS is very diverse and numerous subdivisions havebeen proposed in recent years (Brown M. J., Asbury A. K. (1984) Diabeticneuropathy. Ann.Neurol 15: 2-12). The customary course shows generally astart at the lower extremities in the form of painful malsensationswhich initially occur primarily at night. In further successionsock-like and glove-like sensibility disturbances, loss of depth ofsensitivity, areflexia starting with the achilles cord reflex andfinally pareses should be named, of which the most frequent is theperoneal paresis.

As a result of this diversity of symptoms which mainly occur in combinedform with different dominance numerous attempts have also been made toobjectify the PNS in the last three decades, see for example HoffmannA., Conen D., Leibundgut U., Berger W. (1982) A skin test for automaticneuropathy. Eur Neurol 21: 29-33; Kennedy W. R., Sakuda M. Sutherland D.Goetz F. C. (1984) The sweating deficiency in diabetes mellitus: methodsof quantification and clinical correlation. Neurology 34: 758-763; andWard J. D., Fisher D. J., Barnes C. G., Jessop J. D. (1971) Improvementin nerve conduction following treatment in newly diagnosed diabetes.Lancet i: 428). As one of the few investigations which can be carriedout routinely there remains the measurement of the motoric nerveconduction speed by Ward et al which takes place in the clinical routineat the nervus peronaeus since this is the nerve which is most frequentlyaffected. This diagnostic route however mainly only shows changes whensevere disturbances are already present. However it is precisely at thisstage that the possibilities of therapy are no longer satisfactory.

The object of the present invention is thus to propose a diagnosticmethod and an apparatus for carrying out this method which makes itpossible to recognise neuropathic or polyneuropathic changes at an earlystage, which can be carried out and used in routine operation and whichthus makes a timely therapeutic treatment of the neuropathy possible.Furthermore the method and apparatus should make it possible to achievean objective judgement of the pain sensed by the patient.

The present invention starts from the consideration that the autonomousnerve fibers are generally also affected at a very early stage withpolyneuropathic changes, so that it should be possible to detect thestate of the autonomic nerve fibers via a possible dysfunction of theskin. Thereafter it was speculated that a dysfunction of the skin couldeventually be determined by a change in the microcirculation.

After carrying out microcirculation measurements with several subjectshaving different stages of polyneuropathic diseases it was howeverdetermined that the perfusion values which were found suffers from avery large scatter and that no evaluatable correlation was present withthe degree of the illness. It was then however surprisingly found thaton heating the skin of the individual subject in order to provoke anincrease of the microcirculation the time from the increase of the skintemperature up to the start of the increase of perfusion had a veryreliable correlation with the state of illness found by other methods.The measured time, termed the "hyperthermal perfusion-latency" thusforms a reliable measurement method for determining whether nerve damageis present and the degree of this nerve damage. The hyperthermalperfusion-latency is larger the more severe the nerve damage is at thevessels of the extremity (component of the so-called "autonomous nervesystem"). It was thus found that with severe polyneuropathic syndroms norise in perfusion could be found at all. The hyperthermalperfusion-latency is therefore also no longer measurable there since theperfusion remains at the initial level. This result is however also ofsignificance since one has in this way a confirmation that nerve damageof the most severe degree is present.

Particularly preferred embodiments of the method of the invention and ofthe apparatus of the invention can be found from the subordinate claims.

Particularly advantageous is above all the apparatus of the presentinvention where a computer is used for determining and evaluating thehyperthermal perfusion-latency and for producing a protocol concerningthe measurement which has been carried out. In this way the possibilityexists of carrying out the measurements with relatively untrainedpersonnel and observing the state of a particular patient over a longperiod of time, thus determining the course of his illness and thetherapeutic success by a comparison of the protocols taken over a longperiod of time on different days. This long term evaluation can also beeffected by the computer.

It is particular advantageous with the method and apparatus of theinvention that the measurement can be carried out rapidly and withoutpain for the patient, with the result being extremely reliable andproviding a reliable result even at a very early stage of apoloneuropathy, so that a start can be made at an early stage with thetherapeutic treatment of the polyneuropathy.

A related, however alternative solution of the initially set task isalso provided.

These alternative solutions are based on the recognition that theincrease in temperature of the skin in the region of the heatedextremity, but at a position which is not directly heated, is correlatedwith the perfusion values at or near this position since an increase ofthe perfusion can be equated with an increase of the heat transport bythe blood and thus also with a change in temperature.

A statistical analysis of values measured on subjects has clearlyestablished the correlation.

Advantageous further developments of this alternative solution are alsoprovided by the present invention.

The invention will be explained in more detail in the following withreference to a description of an embodiment of the apparatus of theinvention and also a description of a clinical investigation withreference to the accompanying drawings. In the drawings are shown:

FIG. 1 a schematic illustration of the apparatus of the invention,

FIG. 2 a graphic illustration of the print-out of the computer of FIG.1,

FIGS. 3a to 3c tabelled results of the clinical investigation of 40subjects and indeed with regard to the measured hyperthermalperfusion-latency, initial perfusion values and maximum perfusion valuestogether with their significances in the Wilcoxon test and also in theChi-Square test shown in brackets,

FIGS. 4a to 4c graphic illustrations of the percent median differencesof the three parameters hyperthermal perfusion-latency, initialperfusion values and maximum perfusion values which were determinedduring the investigation, and

FIG. 5 a schematic illustration of an alternative apparatus inaccordance with the invention.

FIG. 1 shows an extremity of a subject in the form of his right foot 10which is covered over with a heated blanket 11 in the ankle region. Theheated blanket 11 is folded around the foot, it could however also be asimple blanket or a heated cushion. The heated blanket is electricallyheated with the electrical energy for heating the heating blanket beingsupplied to the heated blanket via a control circuit 13 and a cable 20.The control circuit 13 is connected to the mains 14 and has a desiredvalue input 15 to which a reference value is supplied corresponding tothe desired temperature of the heated blanket 11, in the present example44° C. The actual temperature of the heated blanket which is determinedby a temperature sensor 16 is applied to an actual value input 17 of thecontrol circuit 13. A temperature probe 18 for determining the skintemperature of the patient is applied directly to the skin of thesubject beneath the heated blanket at the position where it is foldedover. The temperature determined by the temperature probe 18 is appliedvia a lead 19 to an evaluation computer 21.

The temperature probe has a measuring head with a diameter ofapproximately 3 cm and in the middle a small hole. There the laser probe23 of a known laser perfusion measuring apparatus 24 is placed. Thebasic methodology of laser perfusion measurement is described innumerous investigations (see for example Shepherd AP, Riedel GL (1982)Continuous measurement of intestinal mucosal bloodflow by Laser-DooplerVelocimetry. Am J Physiol 242: G699-G672; Stern MD, Lappe DL, Bown PD,Chimosky JE, Holloway GA, Keiser HR (1977) Continuous measurement oftissue blood flow by Laser-Doppler-Spectroscopy. Am J Physiol 232:H441-H448; and Svensson H, Svedman P, Holmberg J, Wieslander JB (1983).Continuous monitoring of circulation in flaps. Transactions of the VIIIInternational Congress of plastic surgery, Montreal, June 26-July 1).The principle of this investigation relates to a Doppler effect which isinfluenced, on the one hand, by the capillary hematokrit and, on theother hand, by the mean flow speed of the particles in the capillaryregion. These two determining parameters are computered into a"perfusion unit" via a computer evaluation. The computer which is usedfor this is accommodated in the laser perfusion measuring apparatus 24.In the present case a PeriFlux PF3 apparatus of the company Perimed inSweden was used for carrying out a perfusion measurement. This apparatusis described in U.S. Pat. No. 4,590,948. The temperature probe is acomponent of the PeriFlux apparatus and is normally used to determinethe temperature at the measuring location and to keep it constant via aheating device and a regulating circuit in order to avoid measurementfalsifications. In the present case the probe was merely used to measurethe temperature.

The measurement values determined from the laser perfusion measuringapparatus 24 "perfusion units" were likewise supplied to the computer 21via the lead 25.

The computer establishes for each subject a protocol in the form of acomputer graphic display showing the changes in the perfusion valueswhich have been found in the form of a percentage of the initial valueas a function of time in seconds from an increase in temperature of thesubject as a result of the action of the heated blanket. This computergraphic display is printed out via a printer 26. The increase in skintemperature is computed as a result of a mean value formation by thecomputer. The time which is important for the present invention, theso-called hyperthermal perfusion-latency is the time from the start ofthe increase in skin temperature, which is caused by the heated blanketat the foot, up to the start of the increase in perfusion as a result ofthe increased skin temperature. The increase in perfusion is alsodetermined by the computer by mean value formation, with only the valuesbeing shown in the graphic display from the determined increase onwards,in order to simplify the picture for the doctor carrying out thetreatment. The protocol of FIG. 2 shows a curve A which applies for ahealthy patient and as curve C the measured increase in skintemperature. All patients for which curves are found which lie on theleft hand side of a curve A can be classified as healthy. If however,the curve found for a specific patient lies to the right hand side ofthe curve A, for example the curve B then this patient suffers from apolyneuropathy. The degree of the polyneuropathy can be determined as aresult of the hyperthermal perfusion-latency which has been found. Inthe present example the hyperthermal perfusion-latency lies at 190seconds in comparison with a value of less than 60 seconds for a healthypatient. With very severe polyneuropathy syndrome no increase in theperfusion can be found at all, the hyperthermal perfusion-latency istherefore also not measurable since the perfusion remains at the initiallevel. The determination that the perfusion has not increased is howeveritself a confirmation that a polyneuropathy syndrome of the most severedegree is already present.

The course of a measurement is as follows. First of all the heating upof the heated blanket to 44° C. is started by closing a switch (notshown). In parallel thereto the laser Doppler flowmetry measurement isstarted. The measurement is carried out for a time period of up to 10minutes and skin temperatures up to 38° are reached. In carrying out themeasurement foot movements of the patient must be avoided as far aspossible since these lead to perfusion changes. Accordingly the curvedetermined by the computer must eventually be judged taking account ofmovement artifacts. These artifacts appear as peak values and are sortedout by the computer and ignored during the mean value formation. Afterdetermining the curve the hyperthermal perfusion-latency can then bemeasured on this curve.

In order to more clearly portray the clinical background to theinvention the result of a clinical investigation of 40 persons will nowbe

40 persons were subdivided in accordance with their clinic into foursubgroups which are set forth in the following: Group 1 included 10healthy subjects (5 men and 5 women) which served as a controlcollective. In group 2 there were 10 patients (6 men, 4 women) which hadsuffered for at least three years from an orally treated diabetismellitus and which sensed frequent or continuous paresthesia, but whichwere however completely unremarkable from their neurological status.Having regard to the known basic disease and the typical anamnesis ithad to be assumed that these complaints represent the start of a PNS("burning feet syndrom"). Group 3 was recruited from a further 10subjects (7 men, 3 women) which had likewise suffered for at least 3years from diabetis mellitus. These nine were set up with an oralantidiabetic medication, one subject was taking insulin. In contrast togroup 2 all patients of this collective had pronounced disturbances ofthe lower extremities in the area of depth sensitivity and surfacesensitivity which could be determined in the neurological status andcould be reproduced at any time. In order to preclude a motoricparticipation a measurement of the nerve conduction speed and of thedistal latency of the nervus peronaeus of the more strongly affectedextremity was carried out electroneurographically. The incorporationinto this group only took place when the nerve conduction speed lay inthe normal region, that is above 41 m/sec. 10 subjects (8 men, 2 women)were combined into the fourth group who showed motoric failures inaddition to sensitivity disturbances. These were verifiedelectroneurographically with reference to a slowed nerve conductionspeed of the nervus peronaeus, likewise at the more strongly effectedlower extremity. Of the subjects 8 received oral antidiabetica, theremaining two were taking insulin.

Methodology

In all subjects the microcirculation of the skin was measured at themore strongly effected lower extremity and observed over a period of 5minutes. At the same time the skin temperature was increased by means ofa special probe which had been heated to 44° C. and the increase inmicrocirculation which could be observed was followed with thepreviously described laser perfusion measurement.

For the statistical evaluation the period from the start of thehyperthermia up to the occurrence of an increase in the microcirculationwas used. This period was termed the so-called "hyperthermalperfusion-latency". Moreover, the initial perfusion value and themaximum value of the microcirculation were determined.

As a significance test there was used, on the one hand, theparameter-free method of Wilcoxon (see for example the book Guilford JP(1959) Fundamental Statistics in Psychology and Education. McGraw-Hill,New York: 587-588) and, on the other hand, the Chi-Square-Test which islikewise described in this book for checking variance differences. Inaccordance with the Wilcoxon test the significance lower limit wasdetermined with p≦0.02. The minimum for the Chi-Square-Text was anchoredat p≦0.001.

Results

40 persons (26 men, 14 women) were included in the investigation. Themaximum age lay in all groups between 55 and 70 years with a relativelylarge scatter. Significant distinctions were not present between the twotests that were used. In all healthy subjects (group 1) the perfusionrose in median after 26 seconds. The median of the hyperthermalperfusion-latency lay in group 2 at 64, in group 3 at 180 and in group 4at 235 seconds. The groups 1 to 3 are distinguished in the Wilcoxon testwith a significance of p≦0.01, the significance between sensory andmotoric PNS (groups 3 and 4) amounted to p≦0.02. All four groups had pvalues of less than ≦0.0001 in the Chi-Square-Test whereby a very gooddifferentiation of the group values is possible.

The initial perfusion values overlapped strongly in the investigatedcollectives which also led to no significance in accordance with theChi-Square-Test. The best differences in this respect were obtainablebetween groups 1 and 4, i.e. between the two extreme groups, however Pwith a value of 0.0016 still lay above the required limit of P≦0.001 forthe Chi-Square-Test. In accordance with the Wilcoxon test thedistinction in these two groups with p≦0.01 was highly significantwhereby it is documented that the most severe form of PNS which was tobe found in this study lay in the perfusion distribution clearly belowthe sound control group. However an association of the individual valueto the respective group is statistically not possible.

The maximum perfusion values show considerably lower values from group 3onwards. Both groups are distinguished highly significantly with p≦0.01from the control group and from group 2 in the Wilcoxon test. In theChi-Square-Test P≦0.0001. Between groups 1 and 2 and also 3 and 4 thesignificant maximum perfusion distinctions could not be found either inthe Wilcoxon test or in the Chi-Square-Test.

A further differentiation into male and female subgroups brought noadditional viewpoints.

The tables 1-3 of FIGS. 3a to 3c represent hyperthermalperfusion-latency, initial perfusion values and maximum perfusion valueswith their significances in the Wilcoxon test and also in theChi-Square-Test in brackets. The graphs 1 to 3 of FIGS. 4a to 4c showthe percentage median distinctions of the three parameters.

Discussions

The results of this investigation clearly indicate that the provocationof the microcirculation by hyperthermia shows distinctions in the stagesof the PNS syndrom. Above all the hyperthermal perfusion-latency is wellsuited for differentiation. The normal collective can be limitedupwardly with hyperthermal perfusion-latency values up to 50 seconds. Acomparison of the individual data for group 2 shows that seven of theten subjects with Burning-Feet-Syndrom lay above this value, thissignifies that three subjects had no pathologically delayed hyperthermalperfusion-latency. On the assumption that actually all subjects of thisgroup had their complaints in the region of an incipient PNS this showsa sensitivity of 70% at this early stage. In the two groups with severepolyneuropathic changes not a single subject had a hyperthermalperfusion-latency value below 50 seconds.

Notable is however not only the increasing slowed hyperthermalperfusion-latency in the individual groups but also the fact that themicrocirculation increase in the two highest PNS groups reducessignificantly with substantially identical initial values. Thus it seemsapparent that the increase of the microcirculation in groups 3 and 4could not be evaluated at all as a true increase but perhaps representsmerely a forced greater microcirculation fluctuation caused by thehyperthermy. From some presently non-published results it appears thatthis is entirely probable, some persons appear only to reach thetemperature which is required to induce a clear increase inmicrocirculation after 10 minutes or more. After 5 minutes ofhyperthermy with a probe at 44° maximum skin temperatures of 36° areachieved, the further increase in temperature then takes place veryslowly.

One must certainly consider that the stimulation of the microcirculationis a result of the autonomous nerve system but the differences of thehyperthermal perfusion-latency in the groups is clear and the frequencyof the autonomic neuropathy has often been investigated and described inconnection with motoric and sensory failures arising with polyneuropathysyndrome, or stated more precisely a separation into individualindependent clinical neuropathy forms is practically impossible, it isalso shown by the frequent attempts to classify this illness.

The hyperthermal laser Doppler flowmetry will certainly not be able todisplace customary electroneurography in the diagnosis of motoric PNSand this was also not the object of this study. Rather thisinvestigation technique makes it possible for the first time to carryout a routine diagnosis and differentiation of the individual stages ofa PNS, and thus under some circumstances to objectively judge a possibletherapeutic success. The diagnosis of a PNS is possible with the aid ofhyperthermal laser Doppler flowmetry at a time when a treatment hasbetter chances of success than at later stages.

FIG. 5 shows an alternative apparatus in accordance with the inventionin which temperature values are measured insted of perfusion values.

The apparatus is in many respects very similar to the apparatus of FIG.1 which is why the same reference numerals have been used for the sameparts. The control circuit for the heated blanket is in particularidentical with that of FIG. 1.

In principal the measurement arrangement is very similar, the laserprobe 23 and also the laser perfusion measuring apparatus 24 are howevernot present and the temperature measurement probe which is used isinsulated relative to the heating blanket 11 which surrounds it. Theskin temperature derived from the temperature probe 18 is applied viathe lead 19 as previously to a microcomputer 21 which records and storesthe variation with time of the skin temperature and determines the risetime between specific temperatures from the variation which has beendetermined and found.

In other words the time is measured here in which the skin temperatureincreases when the heating blanket is heated. Above all temperaturechanges are suitable here in 1° to 2° steps from 30° C. upwards up to amaximum of approximately 36° C.

With light neuropathic changes it has been found, in accordance with theinvention, that the time span for the increase in skin temperature from34° to 36° is extended relative to healthy subjects. For severepolyneuropathic changes a prolongation of the time span between 32° and34° is also found and for very severe forms of polyneuropathy the timespan from 30° to 32° is also increased.

With the heated blanket used for the tests, which has a certain "warm-uptime" until it has fully reached 44° C. the normal regions, i.e. forhealthy subjects, are 50 seconds for 30° to 32°, 30 seconds for 32° to34° and 25 seconds for 34° to 36°. More severe stages frequently do notreach 36° in a measurement period of up to 5 minutes and have forexample a skin temperature latence of 100 seconds or more for 30° to32°.

As a whole measurements have so far been carried out on approximately100 patients and the correlations can be found with hyperthermal laserDoppler flowmetry, above all from 32° C. upwards. When skin temperaturedelays arise amongst these patients to a massive degree then it is foundthat with hyperthermal laser Doppler flowmetry no increase at all canany longer be achieved. Thus one can say that the method with the laserperfusion measurement is admittedly an earlier measurement but also ameasurement which is more subject to disturbances. Muscular tensionscannot be precluded despite good software and are more likely to beincluded. With the temperature measurements they play hardly any role.

In more severe stages a better judgement is possible with thetemperature method since here no increase can be found at all with thehyperthermal laser Doppler flowmetry and thus it is also not possible tomeasure any hyperthermal perfusion-latency. This is important above allfor medication studies.

Finally it should be mentioned that in the embodiment of FIG. 5 thecomputer is also able to establish a protocol in the form of a computergraphic for each subject whereby comparisons can be represented betweena specific patient and a normal patient or for a specific patientbetween the values found before and after treatment, and this computergraphic display can also be printed out via the printer 26.

The apparatus of FIG. 5 has the advantage that it can be manufactured atrelatively favourable cost, since a relatively expensive perfusionmeasurement apparatus is not absolutely essential.

I claim:
 1. A method of determining nerve damage (polyneuropathy) in apatient comprising the steps of:(a) with a heating device increasing thetemperature of a skin portion on an extremity of the patient from afirst temperature to above a second temperature; (b) monitoring thetemperature of said skin portion; (c) taking a first time measurementwhen said second temperature is reached; (d) monitoring perfusion in theextremity at said skin portion while the temperature of said skinportion rises from the second temperature until a predetermined increasein perfusion is noted; (e) taking a second time measurement when saidpredetermined increase in perfusion is noted; (f) subtracting said firsttime measurement from said second time measurement to obtain a perfusiondelay time; and (g) comparing this perfusion delay time with apreviously established reference perfusion delay time; whereby adifference between the measured perfusion delay time in the patient andthe previously established reference perfusion delay time is a measureof the presence and the extent of nerve damage in the patient.
 2. Amethod according to claim 1 wherein the step of monitoring perfusioncomprises the step of directing a laser beam onto said skin portion. 3.A method according to claim 1 wherein the step of taking a first timemeasurement is performed after the temperature of the skin portion hasbeen raised by about 1° C. since the commencement of the heating step.4. A method according to claim 1 including the step of determining thechange in perfusion from the commencement of the perfusion monitoringstep, and discontinuing the perfusion monitoring step when the monitoredperfusion has changed by at least about 10%.
 5. A method according toclaim 4 wherein the discontinuing step is performed when the monitoredperfusion has changed by at least about 25%.
 6. A method according toclaim 1 including the step of establishing the reference perfusion delaytime by performing steps (a) through (e) on a patient having no nervedamage, and subtracting said first time measurement from said secondtime measurement.
 7. A method according to claim 6, wherein the step ofestablishing is performed on a plurality of patients having no nervedamage, and including the step of setting the reference perfusion delaytime based on the results of the establishing step performed on saidplurality of patients.
 8. A method of determining nerve damage(polyneuropathy) in a patient comprising the steps of:(a) with a heatingdevice increasing the temperature of a skin portion on an extremity ofthe patient; (b) monitoring the temperature of said skin portion; (c)taking a first time measurement when the temperature of said skinportion has reached to a first temperature; (d) monitoring perfusion inthe extremity at said skin portion while the temperature of said skinportion rises from the first temperature until a predetermined increasein perfusion is noted; (e) taking a second time measurement when saidpredetermined increase in perfusion is noted; (f) subtracting said firsttime measurement from said second time measurement to obtain a perfusiondelay time; and (g) comparing this perfusion delay time with apreviously established reference perfusion delay time; whereby adifference between the measured perfusion delay time in the patient andthe previously established reference perfusion delay time is a measureof the presence and the extent of nerve damage in the patient.
 9. Amethod of determining nerve damage (polyneuropathy) of a patientcomprising the steps of:with a heating device increasing the temperatureof the skin at a first position on an extremity of the patient from afirst temperature to a second temperature; monitoring the skintemperature at a second position on said extremity, said second positionbeing insulated against direct heating by said heating device; measuringthe amount of time that elapses while the skin temperature at saidsecond position rises from the first temperature to the secondtemperature; and comparing the amount of time measured with a previouslyestablished time interval required to raise the temperature of the skinof another patient known to have no nerve damage from the firsttemperature to the second temperature; whereby a relationship betweenthe measured amount of time and the previously established time intervalis a measure of the presence and of the extent of nerve damage in saidpatient.
 10. A method according to claim 9 including the step ofcommencing the measuring step after said heating device has reached apredetermined, desired temperature.
 11. A method according to claim 10wherein said predetermined temperature of the heating device is about44° C.
 12. A method according to claim 9 wherein said first and secondtemperatures are within the range of 30° C. and 36° C.
 13. A methodaccording to claim 12 including the step of establishing temperaturesub-ranges of 30° C. to 32° C., 32° C. to 34° C., and 34° C. to 36° C.,wherein the step of measuring comprises the step of measuring the amountof time that elapses while the skin temperature at the second positionrises through at least one of said temperature sub-ranges, and whereinthe step of comparing comprises the step of comparing the measuredamounts of time for the skin temperature at said second location to risethrough said temperature sub-ranges with previously established timeintervals for raising the temperature of the skin of the other patientthrough like temperature sub-ranges.